Hall effect sensors are used in a wide variety of applications including industrial and consumer applications. As one example, Hall effect sensors are widely used in the automotive industry for mechanical position sensing, such as gear tooth sensors used in brake systems. Such applications require accuracy.
Hall effect elements or plates experience imbalances due to resistance gradients, geometrical asymmetries and piezoresistive effects which can introduce an offset voltage. The magnitude and polarity of the offset voltage are a function of stresses in the semiconductor from which the element is formed, which stresses vary with mechanical pressure and temperature. Various techniques have been used to address and cancel the Hall offset voltage, including chopper stabilization techniques.
One type of chopped Hall effect sensor includes a switched Hall plate, a chopped amplifier, and a low pass filter. The switched Hall plate, sometimes referred to alternatively as a spinning Hall plate, includes a Hall element having (typically) four contacts and a modulation switch circuit to periodically connect the supply voltage and the amplifier input to one pair of contacts or the other. Quadrature phases of operation are defined by complementary clock signals. Use of such a switched Hall plate provides a way to discriminate the Hall offset voltage (referred to herein as the Hall offset signal component) from the magnetically induced signal (referred to herein as the magnetic signal component). In one such circuit, the switched Hall plate modulates the magnetic signal component and the offset signal component remains substantially invariant. The chopped amplifier demodulates the magnetic signal component and modulates the offset signal component which is then attenuated by the low pass filter to provide the sensor output signal. While this technique is effective to remove the Hall offset voltage, the resulting ripple on the sensor output signal and the sensor response time must be balanced since, the more filtering applied, the lower the resulting ripple, but also the slower the sensor response time.
Some more recent Hall effect sensor applications additionally require faster response times to input magnetic field steps. As one example, Hall effect sensors used in current sensing applications must respond quickly to step changes in the magnetic field, for example in order to rapidly detect fault conditions, such as short circuits in automobile batteries.
One chopped Hall effect sensor that improves upon the above-described sensor in terms of response time is described in U.S. Pat. No. 5,621,319 entitled “Chopped Hall Sensor with Synchronously Chopped Sample and Hold Circuit” which issued on Apr. 15, 1997 to Allegro Microsystems, Inc. of Worcester, Mass., the Assignee of the subject invention. The described sensor includes a switched Hall plate and an amplifier, with the switched Hall plate arranged to modulate the magnetic signal component and maintain the offset signal component substantially invariant. Here, the modulated magnetic signal component is demodulated by sample and hold techniques. According to this technique, signal demodulation is performed by tracking and holding during both clock phases and then inverting the modulated signal during the second phase. In this way, this circuit entirely eliminates ripple on the sensor output signal and thus, provides a faster step response time by avoiding ripple filtering; however, these benefits are achieved at the cost of a degraded signal to noise ratio. This is because the sampling and holding operation can produce noise fold back (i.e., aliasing) since the baseband noise is undersampled.